Piston Sledge
Mirrodin Besieged — uncommon
Artifact — Equipment
Piston Sledge rulings:
2011-06-01: If there are no creatures on the battlefield that Piston Sledge could be attached to when its enters-the-battlefield triggered ability resolves, it remains on the battlefield unattached.
2011-06-01: You can sacrifice Piston Sledge to pay its own equip cost. It won’t become attached as it will be in your graveyard.